This invention relates to the controlled ion implantation doping and etch enhancement of semiconductor materials and flat panel displays by bombardment with selected species of ions having energies in the range 1 keV to 3 MeV.
The development of microelectronics, together with their integrated circuit offsprings, (IC's), represents a major contribution to the revolution that is overtaking societies around the world. Even in their simplest forms, IC's have applications that are so diverse that it is impossible to provide a complete catalogue. Today, even the simplest mechanical devices, such as cooking stoves and washing machines, often include one or more IC's that provide capabilities that were unimaginable just a few decades ago. One impressive example is the hand-held Global Positioning System units (GPS) that provide, at very low cost, latitude and longitude position with an accuracy of a few meters anywhere on the earth.
There are two fundamental exponential "laws" of microelectronics underlying IC manufacture which have been obeyed for at least 30 years. The first is the observation that the transistor density on a silicon chip has grown geometrically for thirty years, doubling every 11/2 years. The second is the "economic miracle" of the decreasing cost per bit of memory devices. The driving potential for this expansion is an outgrowth of two imperatives: One is higher speed, and the second is cost. As a consequence the basic trend is towards ever smaller devices and this trend is expected to dominate the industry for at least another decade.
One of the core manufacturing technologies that has made this scaling of microelectronics practical is the process of ion implantation. Implantation makes possible the creation of three-dimensional electrical circuits and switches with great precision and reproducibility. Ion implantation operates by modifying the electrical properties of well-defined regions of a silicon wafer by introducing selected impurity atoms, one by one, at a velocity that allows them to penetrate the surface layers and come to rest at an appropriate depth.
The characteristics which make implantation such a valuable processing procedure are threefold: First, the concentration of the introduced dopant atoms can be accurately controlled by a straightforward measurement of electrical charge. Secondly, the regions of the base material where dopant atoms are inserted can be precisely defined by photo-resist masks, making possible accurate patterning at ambient room temperature. Thirdly, the implant depth can be adjusted by varying the ion energy.
Presently, implanters are produced in several application specific models and a large semiconductor fabrication site will have several of each type. The types include:
1. High Current Implanters: Typically used for doping at concentration levels &gt;1E15/cm.sup.2 over the energy range 3-80 keV. (These implanters can be used for doses lower than 1E15 and energies higher than 80 keV.) As the name implies, high current capability (10-20 mA) is an essential characteristic for achieving these high dosings at economical throughputs. As feature sizes decrease the lower energy limit of high current implanters is expected to reduce to 1 keV or below; this may require the development of specialized tools. It is anticipated that by the year 2002 approximately 30% of all implants will fall into the high current category. Currently, a majority of commercially available high current implanters operate in the batch-wafer mode but customer pressures are likely to cause the introduction of serial models. PA1 2. Medium Current Implanters: Typically used for doping at concentration levels &lt;2E14/cm.sup.2 over the energy range 20-200 keV. Some applications, such as threshold adjustment, require very high precision. Other recent applications require implanting ions at very large angles to the normal (45-60 degrees) and that this angle be variable during the implantation process. It is anticipated that by the year 2002 approximately 60% of all implants will fall into what is now considered the `medium current class.` Presently medium current implanters are supplied as both serial and batch-wafer devices but serial tools will almost certainly dominate by 2002. PA1 3. High Energy Implanters: Typically used for doping at concentration levels &lt;3E13/cm.sup.2 over the energy range 200-2300 keV. As circuit feature-sizes decrease and the separations between components become smaller the demands for high energy implantation is expected to substantially increase. It is anticipated that by the year 2002 between 5-10% of all implants will be high energy. Currently, both commercially available high energy implanters operate in the batch-wafer mode but customer pressure are likely to push for the introduction of serial tools.
The typical size of the largest versions of these machines is substantial (6 meters.times.3.5 meters) and occupy a significant area of clean room floor space, the annual costs of which may be as high as $50,000/square meter. Thus, while the above mix of implanter models has been accepted by industry there are growing pressures for the development of implanters that have smaller footprints, lower power consumption and that can carry out a very wide range of implantation steps, to allow chained implants, without removing the wafer being processed from the implanter.
There is also a trend in the semiconductor industry to move away from batch processing, where multiple wafers are processed simultaneously, to the processing of individual wafers. To achieve single wafer processing, an implantation apparatus often employs `hybrid scanning.` Here, the ion beam is rastered at high frequency in one direction, using triangular shaped deflection voltage or magnetic field waveforms, and the wafer being processed is implanted by moving it underneath this beam (which may be a "ribbon beam") at a speed that is appropriate to introduce the necessary dopant concentration.